This invention relates to cyclic pressurization systems, such as fuel systems, including cam actuated unit injectors for storage and recovery of fuel pressurization energy.
Designers of fuel systems for diesel engines have come under increasing pressure to achieve ever higher standards of emission abatement while also achieving improved fuel efficiency. It is commonly accepted among such designers that the capability to flexibly adjust injection pressure in the 35 to 200 MPa range is desirable to achieve satisfactory reduction of emissions and increased fuel efficiency. In addition, more precise and predictable control on a cycle by cycle basis (i.e., rapid adjustment) will need to be exercised over various aspects of each fuel injection event such as the metering, timing, pressure, and rate of fuel injection including provision for a pilot injection just prior to the main injection event immediately following the main injection event. At the same time, designers are required to consider the costs associated with the development, manufacture and reliability of any new fuel system since such costs can be staggering not just for design and testing but also for the ancillary costs associated with changing existing engine architecture to accept new types of fuel systems.
Within this context, advanced diesel fuel injection systems are evolving to provide greater flexibility and efficiency in both their application and operation. In recent years, the fuel systems industry has focused attention on the development of energy accumulating, nozzle controlled, fuel system concepts that provide engine speed and load independent control over fuel injection timing, pressure, quantity and multiple injection rate shape. This focused attention has lead to the commercialization of several concepts packaged in the general form of a fluid pressurizing pump connected to a hydraulic energy storage device or high pressure common rail (HPCR) connected to one or more electrically operable injector nozzles. An example of this type of system is disclosed in the commonly assigned International PCT Application WO 94/27041. Other examples include Stumpp et. al. xe2x80x9cCommon Railxe2x80x94An Attractive Fuel Injection System for Passenger Car DI Diesel Engines,xe2x80x9d SAE Technical Paper Series, No. 960870; Guerrassi et. al., xe2x80x9cA Common Rail Injection System for High Speed Direct Injection Diesel Engines,xe2x80x9d SAE Technical Paper Series, No. 980803; and Osenga et al. xe2x80x9cCAT GEARS Up Next Generation Fuel Systems,xe2x80x9d Diesel Progress, August 1998, pp. 82-90.
While these prior art approaches are suitable in many ways, they generally require changes in the architecture of the engine. In particular, the adoption of a high pressure common rail system as a substitute for a fuel system including unit injectors can necessitate a complete redesign of the engine head since the space reserved for the unit injectors is now occupied by an electronically controlled nozzle. At the same time, a high pressure pump is required to be located on the engine in a position permitting a drive connection with the engine crankshaft. This arrangement may require redesign of the gear train at one end of the engine and/or a redesigned camshaft. If the camshaft is changed, various cam driven linkages will likely also require modification.
Numerous examples exist of energy accumulating, nozzle controlled, fuel system concepts employing mechanically actuated unit injectors. For example, see U.S. Pat. No. 5,094,215 to Gustafson; U.S. Pat. No. 5,535,723 to Gibson et al.; U.S. Pat. No. 5,551,398 to Gibson et al.; and U.S. Pat. No. 5,676,114 to Tarr et al. (see FIG. 17). In each of these systems, however, the fuel that is pressurized is fluidically isolated within a single pressurization chamber located within each injector. Still other patents, e.g. U.S. Pat. No. 5,676,114 to Tarr et al. and U.S. Pat. No. 5,819,704 to Tarr et al., describe a flexible and efficient fuel system that is compatible with known types of high pressure common rail (HPCR), unit pump, and unit injector physical forms. None of these references, however, suggests joining injectors or synchronizing pumping. In fact, no known fuel system, commercially available, combines the energy storage and pumping capacities of two or more mechanically actuated unit injectors to form a high pressure, high volume fuel system for supplying fuel under the precise control necessary to achieve reduced emissions and improved fuel efficiency.
A general object of this invention is to provide a fluid pressurizing system that overcomes the deficiencies of the prior art by providing a mechanism including plural mechanically actuated pressurizing units for storing and recovering the energy of pressurization.
Another object of this invention is to provide a fuel system that overcomes the deficiencies of the prior art by providing a mechanism for storing and recovering the energy of fuel pressurization while employing cam actuated unit fuel injectors having dimensional and operating characteristics that permit adoption on existing engines with only minimal changes to the basic architecture of the engine such as the head, cam and injector drive trains.
Another object of this invention is to provide a fuel system that significantly increases the hydraulic energy storage and pumping capacities of mechanically actuated unit injectors that fit within the space provided for more conventional unit injectors.
Still another object of this invention is to provide a fuel system that operates to cyclically impart pressurization energy to and recover pressurization energy from fuel trapped within one or more sets of fluidically linked, synchronously operated unit injectors wherein multiple sets may be operated out of phase of each other by a predetermined angular amount.
Another object of this invention is to provide a fuel system including a plurality of unit injectors wherein each injector has a pressurizing plunger mounted for reciprocation within said bore to form a fuel pressurizing chamber from which fuel may be withdrawn at relatively high pressure for injection into a corresponding combustion chamber of the engine through said injection orifice and wherein a camshaft linkage is provided to synchronously reciprocate the pressurizing plungers of one or more sets of two or more unit injectors as the engine camshaft rotates to impart, pressurization energy to fuel trapped within said fuel pressurizing chambers when said pressurizing plungers advance and to recover pressurization energy from fuel trapped within the fuel pressurizing chambers when the pressurizing plungers retract.
Yet another objective is to provide a fuel system of the type described above including a first interconnecting line for allowing selective fluidic interconnection of the fuel pressurizing chambers formed within a first set of unit injectors to allow fluidic linkage of the volume of fuel being simultaneously pressurized and depressurized within the interconnected fuel pressurizing chambers of a first set of unit injectors, wherein the total volume of fuel that is fluidically linked together within a first set of synchronized unit injectors may be made to substantially exceed the volume of fuel injected during each injection event to avoid substantial loss of injection pressure from the beginning to end of each injection event.
Still another object is to provide a fuel system of the type disclosed above including in association with each set of synchronized unit injectors a first pressure control valve moveable between an open condition in which fuel is allowed to flow in either direction between the source of fuel and the interconnected fuel pressurizing chambers of the set of unit injectors and a closed condition in which energy may be imparted to the fuel within the fuel pressurizing chambers of the set of unit injectors as the corresponding pressurizing plungers are advanced and in which energy may be recovered from the fuel within the fuel pressurizing chambers of a first set of unit injectors as the corresponding pressurizing plungers retract.
Still another object of this invention as described above is to provide a fuel system that may include additional sets of unit injectors with the same capabilities as a first set but are operated out of phase with a first set to allow properly timed fuel injections to occur into each engine combustion cylinder and further including additional interconnecting lines, and synchronized movement of pressurization plungers within the additional sets of unit injectors to cause successive cycles in which pressurization energy is imparted and recovered from a volume of fuel that substantially exceeds the volume of fuel injected during each injection event to avoid substantial loss of injection pressure from the beginning to end of each injection event.
Another object of this invention is to provide a fuel system as described above wherein the pressure control valves and the nozzle control valves associated with sets of unit injectors and unit injectors, respectively, have electro-mechanical actuators (e.g. solenoid or piezoelectric) and the system includes an electronic control unit electrically connected to the valve actuators to cause the following sequential periods of operation for all unit injectors within a set of unit injectors:
a spilling period when the nozzle control valves are in a closed condition, and the pressure control valve is in an open condition and the pressurizing plungers of the set are advancing,
a pressurizing period when the nozzle control valves and the pressure control valve are in closed conditions and the pressurizing plungers of the set are advancing,
an injecting period when one nozzle control valve of an associated unit injection is selectively placed in an open condition while all other nozzle control and pressure control valves remain in closed conditions and while the pressurizing plungers of the set are continuing to advance to cause a controlled amount of fuel to be injected into the combustion chamber of the associated unit injector,
an over pressurizing period when the nozzle control valves and the pressure control valve are in a closed condition and the pressurizing plungers of the set are continuing to advance,
a recovering period when the nozzle control valves and the pressure control valve are in a closed condition and the pressurizing plungers of the set are retracting to cause the pressurization energy to be converted into mechanical energy by the associated plungers and cam shaft lobes, and
a filling period when the nozzle control valves are closed and the pressure control valve is open and the pressurizing plungers are retracting.
Still further, it is an object of the subject invention to provide pressure control signals and nozzle control signals generated for the unit injectors of either of the first or second sets to cause the following sequential periods of operation for each unit injector independent of the operation of the other unit injectors within that set of unit injectors:
a pilot injecting period when the nozzle control valve of a unit injector in one set is in an open condition and the pressure control valve for that set is in a closed condition, and the pressurizing plunger for that unit injector is advancing at a predetermined time in advance of the desired main injection event,
a dwelling period when both the nozzle control valve of an injector in one set and the pressure control valve for that set are in a closed condition and the pressurizing plunger for that unit injector is continuing to advance,
a low-flow main injecting period when the nozzle control valve of a unit injector in one set is in an open condition and the pressure control valve for that set is in a closed condition and the pressurizing plunger for that unit injector is continuing to advance, and
a high-flow main injecting period when the nozzle control valve of a unit injector in one set is in an open condition and the pressure control valve for that set is in a closed condition and the pressurizing plunger for that unit injector is continuing to advance.
Another object of this injection is to provide a fuel system as described above wherein the nozzle control valve of a unit injector can be re-opened to inject an additional amount of fuel following a main injection event while the pressurizing plunger for that unit injector is continuing to advance.
Another object of this invention is to provide a fuel system as described above wherein the low-flow main injection period is initiated at a predetermined point in time during the advance of the corresponding pressuring plunger. The predetermined point in time is selected so that sufficient pressure can be attained just prior to the point at which low-flow main injection is desired.
It is yet another object of this invention to provide a second embodiment of the invention in which a fuel system is provided generally as described above except that the single pressure control valve per set is replaced with a plurality of pressure control valves associated, respectively, with each unit injector of that set. In other words, each unit injector of a set includes its own dedicated pressure control valve. Each pressure control valve has an open condition in which fuel is allowed to flow in either direction between the source of fuel and the corresponding fuel pressurizing chamber of the unit injector and a closed condition in which no fuel is allowed to flow. Each unit injector also includes a shuttle valve having a closed condition in which fuel is prevented from flowing from the corresponding fuel pressurizing chamber into the corresponding interconnecting line whenever the pressure within the corresponding fuel pressurizing chamber is less than the pressure within the interconnecting line and an open condition in which fuel is allowed to flow from the corresponding fuel pressurizing chamber into the interconnecting line The fuel system further includes an electronic control unit for generating the pressure control signals and the nozzle control signals necessary to achieve desired periods of operation. Because each unit injector has its own pressure control valve and shuttle valve, the electronic control unit is able to independently control the timing, rate, quantity and pressure of a separate pilot and main injection from each unit injector within a first set and additional sets. For example, the pumping capacity of two unit injectors in a set may be combined to increase the rate of pressure rise and the fuel delivery rate of one injection event, while a third unit injector is caused to spill fuel to the supply.
It is still another object of this invention to provide a second embodiment as described above wherein the pressure control signals and the nozzle control signals generated for the unit injectors of a first set and additional sets of unit injectors cause the following independent sequential periods of operation for each unit injector:
a spilling period when the nozzle control valve is in a closed condition, the pressure control valve is in an open condition and the pressurizing plunger is advancing,
a pressurizing period when the nozzle control valve and the pressure control valve are both in closed conditions and the pressurizing plunger is continuing to advance,
a pilot injecting period when the nozzle control valve is in an open condition and the pressure control valve is in a closed condition, and the pressurizing plunger is continuing to advance,
a dwelling period when both the nozzle control valve and the pressure control valve are in a closed condition and the pressurizing plunger is continuing to advance,
a low-flow main injecting period when the nozzle control valve is in an open condition and the pressure control valve is in a closed condition and the pressurizing plunger is continuing to advance,
a high-flow main injecting period when the nozzle control valve is in an open condition and the pressure control valve is in a closed condition and the pressurizing plunger is continuing to advance,
an over pressurizing period when both the nozzle control valve and the pressure control valve are in a closed condition and the pressurizing plunger is continuing to advance,
a recovering period when the nozzle control valve is closed and the pressure control valve is closed and the pressurizing plunger is retracting, and
a filling period when the nozzle control valve is closed and the pressure control valve is open and the pressurizing plunger is retracting.
Another object of this invention is to provide a fluid pressurizing system for cyclically imparting pressurizing energy to, and recovering energy from, a fluid by means of a plurality of interlinked pressurizing units such as units that would be used, for example, to hydraulically actuate intake and exhaust valves for an internal combustion engine or to operate material fatigue test equipment.
Yet another object of this invention is to provide a pressure activated, latching,
hydraulic valve with externally referenced reset pressure. In particular, it is an object to provide a shuttle valve to operate in response to the relative magnitude of three separate fluid pressures including Pp which in the pressure of fluid within a corresponding fuel pressurizing chamber, Pl which is the pressure of fluid in an interconnecting line to which the shuttle valve is connected and Pm which is a reference pressure supplied from a source of reference pressure and further wherein the valve may operate in one of four states, including: (1) a line pressurization state in which Pm less than Pp less than Pl when the shuttle valve is closed, (2) a reset state in which Pr=Pp=Pl and the shuttle valve is closed, (3) a energy storage state in which Pm less than Pl less than Pp and the shuttle valve is open, and (4) a energy recovery state in which Pm less than Pp less than P and the shuttle valve is open. It is within the objects of this invention for the valve to take different structural forms in order to achieve the functions described above.
Still other and more detailed objects, features and advantages of the invention may be understood by considering the following Summary of the Drawings and Detailed Description of the Preferred Embodiments.